In the drilling of boreholes, it is often necessary to include a rotating blowout preventor at the upper end of the surface casing. The rotating blowout preventor sealingly receives the kelley in a slidable manner axially therethrough so that the kelley can support and drive the drill string while at the same time fluid can be conveyed through the drill string, downhole to the drill bit, back up through the borehole annulus, where the fluid is discharged from an outlet located at the rotating blowout preventor. In the event a payzone is encountered, the rotating blowout preventor restrains the increased pressures and maintains the flow from the borehole under control, precluding the occurrence of a "blowout".
In the drilling of deep boreholes, it is not unusual for the rotating blowout preventor to fail because one of the many coacting parts thereof has broken or has become unduly worn, as for example, the bearings, a seal, or the stripper rubber. In fact, it is not unusual for the stripper rubber of the rotating blowout preventor to require replacement several times during the drilling of a deep borehole. It would therefore be advantageous to be able to provide a rotating blowout preventor fabricated in such a manner that the various parts thereof, including the stripper rubber, could easily be replaced in the field without the necessity of special tools.
Reference is made to my previous U.S. Pat. Nos. 4,208,056 issued June 17, 1980, and 4,154,448 issued May 15, 1979 for further background of this invention.